Differential torque limiter

ABSTRACT

A differential coupling ( 20 ) has a body ( 21 ), a rotary input member ( 22 ), and two rotary output shafts ( 23, 24 ). The algebraic sum of the angular displacements of the output shafts is proportional to the rotation of the input member. The improvement includes mechanical means ( 39 ), such as a planetary gear ( 42 ), for sensing a torque differential between the output shafts, and a brake ( 38 ) mounted on the body and operatively arranged to selectively brake rotation of the input member, or both output members, when the difference between the torques on the outputs exceeds a predetermined first value.

TECHNICAL FIELD

The present invention relates generally to mechanical actuation systemsfor driving aircraft secondary flight control surfaces, and, moreparticularly, to an improved torque limiter, sensitive to differentialoutput torque, that is particularly adapted to be used in such actuationsystems.

BACKGROUND ARTS

Aircraft flight control surfaces are frequently driven by mechanicalactuation systems. This method of control has been found to be efficientin terms of space and weight, and can inherently provide synchronizationof airfoil surfaces. These mechanical systems generally incorporatetorque limiters so that a jam at one point does not necessarily resultin damage to other parts of the system.

In a typical installation, the system comprises a central power driveunit (“PDU”), which converts hydraulic or electrical power intomechanical power in the form of torque and rotational speed. The PDUwill typically have two mechanical outputs, one for each wing, and eachoutput will be protected with a torque limiter. The torque limiter isset to limit torque to a maximum value, which is typically equal to thetotal torque required for normal operation by the components in onewing, plus a margin of, say, thirty percent, to account for aircraft andflight condition variability and assembly tolerances. If this torquelimit is exceeded, the limiter will lock the PDU input to ground, andall system motion will cease.

The system may drive two or more mechanical actuators in each wing. Ifone actuator jams, it will be subjected to the full torque limit settingthat may be in excess of twice its normal operating load. All of thecomponents of the system must be designed for this large load to preventsecondary damage.

DISCLOSURE OF THE INVENTION

With parenthetical reference to the corresponding parts, portions andsurfaces of the disclosed embodiment, merely for purposes ofillustration and not by way of limitation, the present invention broadlyprovides an improvement in a differential coupling (20) having a body(21), having a rotary input member (22), and having two rotary outputmembers (23, 24), the algebraic sum of the angular displacements of saidoutput members being proportional to the angular displacement of saidinput member, the improvement comprising: a detent mechanism (31, 45,34) operatively arranged to prevent relative angular displacementbetween said output members whenever the difference between the torquesacting on said output members is less than a first predetermined value,and to allow relative angular displacement between said output memberswhenever the difference between the torques acting on said outputmembers is greater than said first predetermined value; a brake (38)mounted on said body and operatively arranged to be selectively appliedto brake rotation of said input member; and a differential mechanism(43) having a mechanical output (44) proportional to the relativeangular displacement between said output members, and operativelyarranged to cause said mechanical output to energize said brake.

The relative angular displacement between said output members may beless than a second predetermined value. The detent mechanism may bearranged to constrain said mechanical output. The differential mechanismmay be operatively arranged to apply said brake in proportion to therelative angular displacement between said output members. Thedifferential mechanism may includes a planetary gear (43) rotatableabout an axis and operatively engaging said output members, and whereinsaid differential mechanism is arranged to operate said brake as afunction of the rotation of said planetary gear about said axis. Themechanical output may be a pin (44) located at an eccentric position onsaid planetary gear, and may further comprise a preloaded springoperatively engaging said pin to establish said first predeterminedvalue.

Accordingly, the general object of the invention is to provide animproved coupling.

Another object is to provide an improved torque limiter, sensitive todifferential output torque.

Another object is to provide protection against secondary system damage,due to downstream jams and disconnects, at a lower system weight thanallowed by the prior art.

Still another object is to provide an improved coupling in whichdifferential motion between two outputs is limited to a predeterminedvalue.

These and other objects and advantages will become apparent from theforegoing and ongoing written specification the drawings, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary longitudinal vertical sectional view of a firstform of the improved coupling, this view showing the input gear, the twooutput shafts, the planetary gear for sensing the difference in torqueson the output shafts, the brake, and the ball-ramp input torque sensor.

FIG. 2 is an enlarged fragmentary horizontal sectional view thereof,taken generally on line 2—2 of FIG. 1, and particularly showing theplanetary gear and eccentric pin.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

At the outset, it should be clearly understood that like referencenumerals are intended to identify the same structural elements, portionsor surfaces consistently throughout the several drawing figures, as suchelements, portions or surfaces may be further described or explained bythe entire written specification, of which this detailed description isan integral part. Unless otherwise indicated, the drawings are intendedto be read (e.g., cross-hatching, arrangement of parts, proportion,degree, etc.) together with the specification, and are to be considereda portion of the entire written description of this invention. As usedin the following description, the terms “horizontal”, “vertical”,“left”, “right”, “up” and “down”, as well as adjectival and adverbialderivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”,etc.), simply refer to the orientation of the illustrated structure asthe particular drawing figure faces the reader. Similarly, the terms“inwardly” and “outwardly” generally refer to the orientation of asurface relative to its axis of elongation, or axis of rotation, asappropriate.

Referring now to the drawings, and, more particularly, to FIG. 1thereof, the present invention provides an improved coupling, generallyindicated at 20. The improved coupling is shown as having an assembledbody, generally indicated at 21, a rotary input member 22, and left andright rotary output shafts 23, 24, respectively. The input member andoutput shafts are severally mounted on the body formation abouthorizontal axis x-x. The algebraic sum of the rotations of output shafts23, 24 is proportional to the rotation of input member 22.

The assembled body is shown as broadly including (from left to right inFIG. 1) an end cap 25, a stop plate 26, a main housing 28, and a bearingsupport 29. These various body parts are suitably assembled andconnected as shown to form the body assembly.

The input member 22 is a specially-configured member having an outerspur gear 30. An annular cam member 31 is shown as surrounding the leftmarginal end portion of input member 22 within the body. A cylindricalcarrier member 32 is arranged radially inwardly of the input member.This carrier member 32 has near its center a splined connection,indicated at 33, with cam member 31. Thus, members 31 and 32 areconstrained to rotate together. However, splined connection 33 permitscam member 31 to move axially relative to carrier member 32. A spring 34acts between appropriate shoulders provided on the input member 22 andcam member 31, and urges cam member 31 to move rightwardly relative tothe input member. A ball 35 is restrained between facing conicalrecesses extending into the input member 22 and cam member 31,respectively. This arrangement constitutes means, generally indicated at36, for operating the brake, generally indicated at 38, in the eventthat the input torque exceeds a predetermined value.

Brake 38 is shown as having a plurality of interdigital disks, withalternating disks being connected to the body and to cam member 31,respectively, by means of various spline connections. Thus, if there isrelative rotation between input member 22 and cam member 31, ball 35will ride up on its conical seats, and will displace cam member 31leftwardly against the opposing bias of spring 34 to exert a clampingforce on the relatively-rotating disks of the brake assembly. Thisclamping force will produce a braking torque between the input memberand the body.

The improved coupling also includes means, generally indicated at 39,for sensing the difference between the torques on the output shafts 23,24. As best shown in FIG. 1, these two output shafts are hollow. Theleft shaft 23 has a spur gear 40 at its right marginal end, and theright shaft 24 has a similar spur gear 41 at its left marginal end. Aplanetary gear, generally indicated at 42, has a generally-cylindricalbarrel that extends outwardly along a radial axis. The radial inward andoutward ends of the planetary gear are received in journal bearingswithin carrier member 32. Gears 40 and 41 are in meshing engagement witha circumferential gear teeth, generally indicated at 43, mounted on theplanetary gear. A pin 44 extends radially outwardly from the upper endface of the planetary gear at a location eccentric to the axis ofplanetary gear 42.

Thus, if output shafts 23 and 24 rotate together in the same directionand at the same angular speed, planetary gear 42 will not rotate aboutits axis. However, if there is relative rotation between output shafts23 and 24, then gear 42 will rotate about its radial axis. Eccentric pin44 will then swing in an arc about the axis of gear 42, and willdisplace member 45 leftwardly relative to carrier member 32. Sincemember 45 has a hooked engagement with the left marginal end portion ofcam member 31, such leftward movement of member 45 will produce acorresponding leftward motion of cam member 31, to again exert aclamping force on brake 38. Spring 46 acts between a rightwardly-facingshoulder on a leftward extension of carrier member 32 and the left endface of member 45.

Thus, during normal operation, input member 22 is rotated about couplingaxis x-x. If the torque on the output members is less than apredetermined torque, then ball 35 remains seated between the facingconical seats provided on cam member 31 and input member 22. Hence,rotation of input member 22 will normally cause corresponding rotationof cam member 31 and carrier member 32. Suitable bearings are providedon the body to accommodate this rotation. If members 31 and 32 rotatewith the input member, and if there is no relative rotation between thetwo output members, then the two output members will simply rotatetogether about axis x-x.

However, if there is a differential torque on the output members 23, 24that causes relative rotation therebetween, then the several planetarygears 42 will rotate about their respective axes. The eccentric pins 44mounted on these planetary gears will then displace member 45leftwardly, overcoming the bias of spring 46. This will, in turn,displace cam member 31 leftwardly against the bias of spring 34, andwill cause a frictional engagement of the relatively-rotating brakedisks. Thus, in the event that a differential torque on the outputshafts causes relative rotation therebetween, such relative rotationwill produce a braking action on the two output shafts and on the inputshaft.

Alternatively, if the input torque exceeds a predetermined value, thenball 35 will ride up on its facing conical seats, and displace cammember 31 leftwardly to cause a similar braking action.

Modifications

The present invention expressly contemplates that many changes andmodifications may be made. For example, while the output shafts areshown as being hollow, they may alternatively be solid. Similarly, themeshing differential gears of the planetary members and the two outputmembers could bevel gears, instead of the spur gears shown in thedrawings. Also, the improved coupling could be designed to limit at adifferent differential torque value for each of the two outputs. Thiscould be achieved by providing two separate gears with differing toothcounts, displaced axially along each planetary member and engagingseparately with the two output members. The planetary gear and eccentricpin are only one possible means for sensing a torque differentialbetween the output shafts. The input member may be a gear or some othertype of mechanism. The number and configurations of the planetary gearsmay also be changed. Similarly, the structure of the brake mechanism maybe also changed or modified, as desired. One alternative would be acapstan-spring type of brake mechanism, and a second alternative wouldbe a differential ball-ramp-plate type of brake. Both of thesealternative mechanisms would be operated directly by the differentialtorque and motion of the two output members, and not by the eccentricpin-planetary gear mechanism shown in the drawings. Similarly, thecapstan-spring mechanism could be arranged to brake both output shaftssimultaneously, or the input member. The differential ball-ramp-plateimplementation may be arranged to brake either the input or bothoutputs.

Therefore, while the presently-preferred form of the improveddifferential coupling has been shown as described, and severalmodifications thereof discussed, persons skilled in this art willreadily appreciate that various additional changes and modifications maybe made without departing from the spirit of the invention, as definedand differentiated by the following claims.

What is claimed is:
 1. In a differential coupling having a body, havinga rotary input member and having two rotary output members, thealgebraic sum of the angular displacements of said output members beingproportional to the angular displacement of said input member, theimprovement comprising: a detent mechanism operatively arranged toprevent relative angular displacement between said output memberswhenever the difference between the torques acting on said outputmembers is less than a first predetermined value, and to allow relativeangular displacement between said output members whenever the differencebetween the torques acting on said output members is greater than saidfirst predetermined value; a brake mounted on said body and operativelyarranged to be selectively applied to brake rotation of said inputmember; and a differential mechanism having a mechanical outputproportional to the relative angular displacement between said outputmembers, and operatively arranged to cause said mechanical output toenergize said brake.
 2. The improvement as set forth in claim 1 whereinthe relative angular displacement between said output members is lessthan a second predetermined value.
 3. The improvement as set forth inclaim 1 wherein said detent mechanism is arranged to constrain saidmechanical output.
 4. The improvement as set forth in claim 1 whereinsaid differential mechanism is operatively arranged to apply said brakein proportion to the relative angular displacement between said outputmembers.
 5. The improvement as set forth in claim 1 wherein saiddifferential mechanism includes a planetary gear rotatable about an axisand operatively engaging said output members, and wherein saiddifferential mechanism is arranged to operate said brake as a functionof the rotation of said planetary gear about said axis.
 6. Theimprovement as set froth in claim 5 wherein said mechanical output is apin located at an eccentric position on said planetary gear, and furthercomprising a preloaded spring operatively engaging said pin to establishsaid first predetermined value.